Friction pair adapted to operate without lubrication



Aug. 4, 1970 J. L. POLTI 3,522,974

FRICTION PAIR ADAPTED TO OPERATE WITHOUT LUBRICATION Filed June 20, 1968 160 260. sbo 460 500 600 760 800A 1 /V//E/V 70/: 12 J54 100, #007 United States Patent ice US. Cl. 3083 6 Claims ABSTRACT OF THE DISCLOSURE A pair of metallic members adapted to work in rubbing contact without lubrication, being resistant to wear and to corosion, in which one of the rubbing parts of said pair is constituted by metallic gold of 3 to 20 microns in thickness, the other rubbing part being formed by a mixture of chromium and chromium oxide. The metals in rubbing contact may be separated from the base metal by one or several metals which are soluble in each other.

The present invention has for its object a friction pair without lubrication, resistant to wear and to corrosion, and capable of working without seizure in various surrounding media: air, water, vapour or gas, corrosive fluids, oxidizing media, etc.

This friction pair is characterized in that one of the parts in rubbing contact is constituted by gold and the other has a chromium base.

In order to produce this pair, the superficial parts in rubbing contact, of gold or with a chromium base, are preferably deposited on the base 'metal through the intermediary of a layer of hard metal.

Thus, the rubbing member of gold, formed by a coating of gold of 3 to 20 microns in thickness, is deposited on a coating of nickel which is in turn fixed to the base metal of the part.

The rubbing member of chromium or mixture of chromium and chromium oxide, is formed either by a direct deposit of chromium on the base metal if the latter is capable of forming an alloy with chromium, or through the intermediary of successive layers of metals which are soluble in each other, such as nickel and cobalt in particular.

The invention is illustrated by the accompanying drawings, in which:

FIG. 1 is a view in cross-section of the arrangement of the friction pair;

FIG. 2 is an explanatory curve;

FIGS. 3 and 4 represent the application of the elements of the pair;

FIG. 5 shows diagrammatically a device for testing the friction pair.

As shown in FIG. 1 of the accompanying drawings, the first part A of the friction pair comprises, starting from the interior towards the exterior:

The base metal 1, capable of forming alloys with nickel;

An intermediate layer 2 of nickel, the thickness of which is determined in dependence on the hardness of the base metal 1;

A surface coating 3 of gold having a thickness comprised between 3 and 20 microns.

The thickness of the layer of nickel is chosen between two extreme limits, as indicated in the graph shown in FIG. 2 of the accompanying drawings. This graph has plotted in abscissae the hardness A of the base metal 1, expressed in Vickers, with a load of 25 grams, and in ordinates the thickness e of the layer of nickel in microns. The thickness of the nickel layer is chosen to have a value 3,522,974 Patented Aug. 4, 1970 located within the zone a included between the two curves b and c.

The second part B of the friction pair comprises, from the interior towards the exterior, as shown in FIG. 1 of the accompanying drawings:

The base metal 4 chosen so as to be capable of forming alloys with chromium;

An intermediate layer 5 formed by any compound of chromium and one or several other (metals, one of which may be the base metal itself;

A surface coating 6 formed by a mixture of chromium and chromium oxide having a thickness less than 2 microns.

The thickness of the hard layer 5 is greater than 10 microns; its hardness passes through a maximum value in a zone comprised between 0.01 and 0.5 mm. below the surface, and then decreases farther towards the interior, so as gradually to attain the hardness of the centre of the base metal. This maximum hardness of the intermediate layer is greater than 400 Vickers at 25 grams.

The surface layer 6 is obtained by polishing or grinding or any other means producing friction, preferably carried out dry and in an oxidizing atmosphere, this atmosphere being oxygen or even the surrounding atmosphere. It is beneficial to permit the part to heat-up freely during the course of this operation. The surface layer 6 can also be obtained by any desired method which produces surface oxidation. The roughness of this surface layer must not exceed a value of 20 micro-inches 0f the CLA standard (Centre Line Average).

In an alternative form of the pair according to the invention, the intermediate layer 5 produced on the part B is chromium. In this case, if the base metal constituting this part B only forms alloys with chromium with difficulty, there will be interposed between them successive layers of metal, in such manner that each of them is simultaneously soluble in that which precedes it and in that which follows it, the first directly in contact with the base metal being soluble in this latter, and the last being directly in contact with the chromium and consisting of nickel or cobalt, preferably nickel. The respective thicknesses of the various successive layers thus interposed between the base metal and the layer of chromium will be comprised between 0.5 and 10 microns.

In the application of the pair according to the invention, the use of gold and the mixture of chromium and chromium oxide for one or the other of the two surfaces is determined as a function of the kinematic conditions of use of the parts in contact. If one of the surfaces is closed, that is to say wholly traversed during one cycle by the supporting zone, the gold will be applied to this closed surface. In such case, the chromium will be applied to the open surface, that is to say to that which is not wholly traversed during one cycle by the supporting zone; this is the case for example represented by FIG. 3 of the accompanying drawings, in which a shaft 10 rotates in a bearing. 11, the load carried by the shaft having a fixed direction indicated by the arrow F.

In this case, the shaft 10 is gilded and it is the surface of the bearing 11 which is coated with a mixture of chromium and chromium oxide. If, contrary to the preceding case, none of the surfaces falls within one of the closed or open classifications, the gold will be applied to that of the two surfaces on which the supporting zone effects the longest travel. This is the case for example shown in FIG. 4 of the accompanying drawings, in which a saddle 13 is in rubbing contact with a slide 12, and in which the gold is applied to the slide and the mixture of chromium and chromium oxide to the saddle.

The friction pair according to the invention finds its best field of use in cases of operation under free oxidation and heating, the friction ensuring the constant regeneration of the surface layer formed by chromium and chromium oxide mixed together. In the contrary case, the rubbing contact is only good as long as this surface layer subsists.

The invention will be illustrated in the non-limitative examples given below, which give the comparative results of tests carried out on a friction machine in which, in accordance with FIG. 5 of the accompanying drawings, a ring 14 of 35 mm. in diameter is caused to rotate at a variable speed and with an adjustable load, bearing on a supporting plate 15 which is given a uniform alternating linear motion having an amplitude of 18 mm.

EXAMPLE 1 The ring and the plate are of semi-hard annealed carbon steel XC having the composition: 0.36% C.; 0.28%

Si; 0.55% Mn, the remainder being iron. The ring (closed surface) is first of all nickel-plated and then gold-plated; the plate (open surface) is chromium-plated and its roughness is 15 micro-inches CLA, obtained first by polishing with abrasive paper and then by polishing with alumina carried out in the ambient air, leaving the part to heat-up freely.

The load which applies the small plate against the ring is 24 daN and the speed of slip is 0.075 m. per sec. The part, previously de-greased with ethyl acetate is in rubbing contact in the ambient atmosphere. Under these conditions, the rubbing action can be continued for 3 hours with a coefficient of friction of 0.18, without any deterioration of the surface conditions and without showing any trace of corrosion.

EXAMPLE 2 EXAMPLE 3 The ring is again identical with those of Examples 1 and 2. The plate is of stainless steel, type Z3 CH 18.10 having the composition: 0.024% C; 0.58% Si; 0.76% Mn; 11.5% Ni; 19.3% Cr; 023% Mo; 0.02% Ti, the remainder being iron. On this plate, a layer of chromium is deposited by electrolytic means, while interposing between the stainless steel base and the surface coating of chromi- 5 urn an intermediate layer of nickel. The surface thus 01)- tained is then polished, following the method of operation described in the previous examples.

When thus treated, the parts can be in rubbing contact with a load of 35 daN and with a speed of slip of 0.5 m. per sec. in ambient air without any trace of oil or grease for one hour with a coefficient of friction of 0.15, without any deterioration of the surface condition and without any corrosion.

What I claim is:

1. A friction pair adapted to operate without lubrication, being resistant to wear and to corrosion, in which one of the rubbing parts of said pair is constituted by gold while the other is constituted by a mixture of chromium and chromium oxide, said rubbing parts being each fixed on a metal base.

2. A friction pair as claimed in claim 1, in which said rubbing parts are fixed on said metal base through the intermediary of a layer of hard metal.

3. A friction pair as claimed in claim 1, in which said rubbing member of gold is constituted by a layer of 'gold 3 to 20 microns in thickness, deposited on a layer of nickel which is fixed on said metal base.

4. A friction pair as claimed in claim 1, in which said rubbing member constituted by chromium and chromium oxide is fixed on the metal of the base through the intermediary of a hard layer of chromium.

5. A friction pair as claimed in claim 1, in which said rubbing member constituted by chromium and chromium oxide is fixed on the metal of the base through the intermediary of a hard layer of chromium alloy.

6. A friction pair as claimed in claim 1, in which said rubbing member constituted by chromium and chromium oxide is fixed on a layer of chromium which is separated from the metal of the base by a layer of metal selected from the group consisting of nickel and cobalt.

References Cited UNITED STATES PATENTS 1,869,412 8/1932 Devore 308241 2,024,150 12/1935 Davignon 29--189 2,179,824 11/1939 Kip. 2,241,789 5/1941 Queneau 308237 X 2,247,755 7/1941 Hensel. 2,477,139 7/1949 Patton 308237 3,297,552 1/1967 Gisser 29-198 FOREIGN PATENTS 467,397 6/ 1937 Great Britain.

1,023,007 3/1966 Great Britain.

MARTIN P. SCHWADRON, Primary Examiner L. L. JOHNSON, Assistant Examiner U.S. CL. X.R. 308237, 241 

